1. Field of the Invention
The present invention relates to a deflection yoke apparatus for use in a color CRT and display device.
2. Description of the Related Art
A recent tendency of a CRT (hereinafter referred to merely as CRT) for color reception has been toward broadening a deflection angle and flattening a screen panel and, at the same time, improving the quality of an image. A deflection yoke system for CRT is normally of a convergence-free type. A pincushion-free system has also been increasingly utilized which eliminates the need to provide an extra deflection deformation correction circuit.
In a deflection yoke apparatus for convergence-free and pincushion-free systems, horizontal deflection coils create pincushion type magnetic field distributions so as to achieve a convergence-free state, and vertical deflection coils are so arranged as to provide barrel-type magnetic field distribution. A pair of magnetic pieces CROSS ARMS, right and left, are provided on the front-side section of deflection yoke DY in order to mainly correct for right and left pincushion distortion areas.
The broader the angle at which an electron beam is deflected and the flatter the panel screen, the greater the upper and lower, right and left pincushion distortion areas. It is, therefore, normally necessary that, in order to correct for the pincushion distortion, a more intense pincushion distortion pattern must be obtained as a front-side magnetic field distribution on the deflection yoke apparatus.
If, in order to gain a pincushion type magnetic field distribution, a measure is taken with the winding distributions, etc., of the horizontal and vertical deflection coils per se, then a vertical misconvergence (M-PQV) is increased in a middle of those right and left end sides of the screen. The vertical misconvergence (M-PQV) can be decreased to some extent by adjusting the winding distribution of the horizontal deflection coils, but there is a limit on the achievement of such a decrease of the vertical misconvergence involved. Therefore, a countermeasure is taken through a balance between M-PQV and PQV, where PQV is a vertical misconvergence at the corners of the Ranel screen. For example, if the vertical misconvergence (M-PQV) is decreased through the adjustment of the winding distributions in the horizontal deflection coils, then the vertical misconvergence at the corners of the image screen PQV is increased.
In the deflection yoke apparatus for the display device, etc., an attempt has been made to provide a correction circuit as, for example, in Published Examined Japanese Patent Application H-1-29018 so that correction may be made for misconvergences M-PQV and PQV. In this case, the resultant apparatus becomes expensive due to the addition of the correction circuit.
According to the conventional apparatus, as set out above, the misconvergences PQV and M-PQV become larger and, in additional case of an extra correction circuit, a higher cost is involved.